Abstract
This paper reports a new route to synthesize calcium carbonate (CaCO3)-based nanoscale ionic materials (NIMs) via an in situ formation method to form the CaCO3 nanoparticles with a polysiloxane quaternary ammonium salt (PQAC) corona (PQAC-CaCO3 nanoparticles), followed by an ionic exchange reaction to fabricate a poly(ethylene glycol)-tailed sulfonate anion (NPEP) canopy. The chemical compositions and structures of the CaCO3-based NIMs synthesized in this work were confirmed by Fourier-transform infrared spectroscopy and solid-state 13C NMR spectroscopy. Transmission electron microscopic observation indicated that the CaCO3-based NIMs presented a rhombohedral shape with a well-defined core-shell structure, and they also obtained an NPEP canopy with a thickness of 4–6 nm. X-ray powder diffraction investigation confirmed that the CaCO3 inner core had a calcite crystalline structure, whereas the NPEP canopy was amorphous. The NPEP canopy was found to show a characteristic crystallization–melting behaviour in the presence of the ion bonding with PQAC-CaCO3 nanoparticles according to the characterization of differential scanning calorimetry. Thermogravimetric analysis indicated that the CaCO3-based NIMs achieved a high content of NPEP canopy as well as an improvement in thermal stability owing to the ion-bonding effect. Most of all, the CaCO3-based NIMs demonstrated a liquid-like behaviour above the critical temperature in the absence of solvent. Moreover, the CaCO3-based NIMs also showed a relatively high electrical conductivity with a temperature dependency due to the ionic conductive effect. This work will provide a more feasible and energy-saving methodology for the preparation of CaCO3-based NIMs to promote their industrialization and extensive applications.
Highlights
Nanoscale ionic materials (NIMs) are a type of nanoparticles with liquid-like behaviour in the absence of solvent, which were pioneered by Giannelis et al [1]
It is interestingly observed from figure 2c,e that, after capping the PQAC-CaCO3 nanoparticles with an NPEP canopy, the resulting CaCO3-based NIMs exhibit a well-defined core-shell nanostructure, in which a thin outer layer with comparably low contrast can be distinguished to sheath a denser inner core [31]
The CaCO3-based NIMs were synthesized via an in situ formation method to form the PQAC-CaCO3 nanoparticles, followed by an ionic exchange reaction to fabricate an NPEP canopy, and their chemical compositions were confirmed by Fourier-transform infrared (FTIR) spectroscopy and solid-state 13C NMR spectroscopy
Summary
Nanoscale ionic materials (NIMs) are a type of nanoparticles with liquid-like behaviour in the absence of solvent, which were pioneered by Giannelis et al [1]. NIMs are typically composed of an inorganic nanosized core, a covalently tethered ionic corona and an ionically tethered oligomeric canopy, and they have a core–corona–canopy structure [3]. Such a structural feature leads to homogeneous fluids rather than a dual-phase dispersion of nanoparticles suspended in organic liquids and makes NIMs achieve flow properties that span the range from glassy solids to freeflowing liquids [4], and their solvent-free fluidity with zero vapour pressure offers a new prospect in scientific and technological applications. NIMs have been broadly applied as functional ionic liquids [11], liquid CO2 absorbents [12], highly lubricative dispersions [13] and functional coatings with controlled surface properties [14], and they can be used as electrolytes for lithium-ion batteries [15], precursor materials for highly porous separation films [16] and good candidate materials for various sensors [17]
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